By contrast, there were 16,319 in that age bracket going into the 2016 federal election, and according to The Sun-Herald, under-30s are now a "faster growing bloc of voters" in that electorate than over 70s, despite the area's reputation as a hub for older Aussies.

That spike in youth enrolment might not seem huge, but according to some, it could be enough to cost Mr Abbott the "safe" seat he has held since 1994.

Last March, the high-profile grassroots "Vote Tony Out" campaign was launched with the sole purpose of ousting the sitting member.

The group has now thrown its support behind independent Zali Steggall - and organiser Mark Kelly said he was now "100 per cent" confident the former Olympian would win the primary vote on Saturday.

He told news.com.au the average age of a Warringah voter was now 38, and that there had been an "influx" of under-25s enrolled in the seat.

He said most younger voters were passionate about topics such as tackling climate change and marriage equality - and Mr Abbott's tough stance against action on these issues could finally topple his reign.

"It's on - I can't wait until Saturday night," he said.

"Tony's days are numbered down to five … I don't know anyone who is voting for Tony Abbott."

Mr Kelly predicted a massive "protest vote" against Mr Abbott in favour of Ms Steggall, and said most of the sitting member's supporters actually lived outside the electorate - meaning they wouldn't be able to vote for him on the day.

Warringah candidates Tony Abbott and Zali Steggall will go head to head on Saturday. Picture: Damian Shaw

"There has been a gradual trend with the electorate getting younger … with a lot of young families moving in to suburbs like Mosman and Manly," he said.

"Abbott is aiming at a typical conservative, older voter, but that person probably isn't around here anymore."

In 2017, a staggering 75 per cent of Warringah constituents voted "yes" in the marriage equality plebiscite - the fourth highest Yes vote in the state - despite Mr Abbott's staunch opposition.

Mr Kelly said Mr Abbott's decision to walk out of parliament instead of voting on the marriage equality bill when it reached the House of Representatives was a "slap in the face" local voters hadn't forgotten.

He said young people were now as mobilised and politically engaged as they had been during the Vietnam War - and they couldn't understand why politicians like Mr Abbott were "ignoring" their views on things such as refugee rights, the environment and equality, which were no longer "progressive", but mainstream.

"If you go to a Liberal Party event, it is only old white blokes who go and that's why they're out of touch," Mr Kelly said.

"Tony Abbott is like a grandfather trying to be involved in the family business still. Times have moved on, but he's got his abacus out trying to balance the till every afternoon."

That means 16.4 million of us will be eligible to vote on Saturday, thanks in part to the rush of people adding themselves to the roll in order to participate in the 2017 same-sex marriage plebiscite.

McCrindle social researcher Ashley Fell told news.com.au 728,000 Australians had also reached voting age since the 2016 federal election - and this huge demographic of new Gen Z voters were a "force to be reckoned with", with 12 per cent of the voting population now aged under 24.

She said younger people tended to be more socially progressive yet economically conservative, which could impact the election outcome.

"Young people today are more tuned into matters like climate change; they are more socially progressive and were more likely to vote Yes in the plebiscite," she said.

But she said while that demographic was more involved in "political activism" relating to certain causes, they were also more "apathetic" towards traditional politics.

That's likely caused by the recent revolving door of Australian prime ministers - which Ms Fell said could inspire Gen Z to turn away from the major parties and towards "niche parties" and independents that were able to engage with them.